The basic idea regarding vehicle and pedestrian movements is that the system can be entirely pretimed (interval control) or divided up into phases (phase control). The typical idea of operation is that any compatible phases should be able to run concurrently so long as there is time available. During Pedestrian Walk and Clearance time however these phases cannot be forced off or timed out. (Otherwise people could get hit by cars) This limits the amount of time the button can be pressed during a green light and still change the pedestrian signal.
The basic idea regarding vehicle and pedestrian movements is that the system can be entirely pretimed (interval control) or divided up into phases (phase control). The typical idea of operation is that any compatible phases should be able to run concurrently so long as there is time available. During Pedestrian Walk and Clearance time however these phases cannot be forced off or timed out. (Otherwise people could get hit by cars) This limits the amount of time the button can be pressed during a green light and still change the pedestrian signal.